1. Field of the Invention
The present invention relates to a process for the preparation of polyether-ester polyols. More particularly, the invention relates to the preparation of these polyols by reacting a polyether polyol, tetrahydrophthalic anhydride and an alkylene oxide in the presence of an effective amount of a catalyst selected from the group consisting of calcium naphthenate and cobalt naphthenate.
2. Description of the Prior Art
The preparation of polyether-ester polyols by the reaction of an alkylene oxide with a half acid ester obtained by the reaction of a polyol with an unsaturated acid anhydride is well known in the art as taught in U.S. Pat. Nos. 3,931,092, 4,014,846, 4,093,573 and 4,144,395. These patents relate to uncatalyzed or trialkylamine-catalyzed reactions. U.S. Pat. No. 3,374,208 teaches the use of various metal catalysts for the preparation of polyesters. The prior art, however, does not teach the preparation of polyether-ester polyols having an acidity of less than 1 mg KOH/gm of sample employing the process of the instant invention.